Reverse current evolution during fuel cell start-up: Integrating high-resolution segmented current measurement with quasi-2D equivalent circuit modeling

During the start-up process of proton exchange membrane fuel cells (PEMFCs), transient reverse currents may emerge inside the stack, leading to localized catalyst layer decay and nonuniform performance degradation. Understanding the transient internal current evolution during start-up is crucial for improving fuel cell durability. In this study, a self-designed 33 × 12 segmented current measurement device with high spatial and temporal resolution is developed to investigate the transient reverse current behaviors under different start-up conditions. The transient wave-like internal current distributions are experimentally observed inside a commercial-sized PEMFC and visualized with 3D images during the start-up process within several seconds. To further understand the reverse current formation mechanism, a quasi-2D equivalent circuit model is established and optimized through parameter identification using the Sequential Parameter-wise Transfer Bayesian Optimization framework. The numerical results exhibit good agreement with experimental measurements, achieving a mean absolute error as low as 2.95 mA/cm2, and effectively reproducing the detected transient wave-like internal currents. It is found that the duration of transient reverse currents and the local reverse coulombic charge increase progressively toward the anode outlet. The cathode catalyst carbon support around the anode outlet suffers the most severe corrosion during the start-up process, leading to nonuniform performance degradation. Furthermore, increasing the H2 flow rate from 6.6 L/min to 19.6 L/min is shown to reduce the local reverse coulombic charge by over 70 %, which is a key factor in mitigating cathode catalyst corrosion. The comprehensive investigation of the transient reverse current evolution provides insights to optimize start-up control strategies and fuel cell designs for extended lifespan.